In blood group serological diagnostics, parameters are generally tested which are of particular relevance in the context of transfusions or of morbus haemolyticus neonatorum (Mhn). This includes inter alia the detection of antigens on the surface of erythrocytes which are characteristic for the blood groups. Further important antigen systems are present also on thrombocytes, granulocytes, lymphocytes which likewise play a role in the context of transfusions and/or transplantations.
It is known that for determining blood group antigens the erythrocytes of the persons to be tested, (donors or recipients) are brought together with reagents which contain blood group specific antibodies. Generally these tests are performed in the liquid state, in which by mixing of an erythrocyte-containing sample with a sample containing antibodies directed against a specific blood group characteristic a testing batch is produced. The testing batch is then incubated over a defined period and under defined conditions and after conclusion of the incubation, either directly or after a centrifugation step, is tested visually or by optical methods for a possible agglutination or adsorption of the erythrocytes. The predominant end point measurement in blood group serology is still the hemaglutination test. For each blood group to be determined a separate batch must be pipetted, i.e. e.g. for the determination of the nine most important blood groups A, B, D, C, c, E, e, Cw and K, nine separate batches are needed, without counting any control.
Lateral flow tests nowadays are frequently applied as quick tests e.g. as pregnancy tests, for determining infection markers or for drug screening. A lateral flow test device in a known manner includes a rigid support on which an application zone for the sample to be tested is provided, a separating membrane, on which bonding elements, e.g. catcher antibodies or antigens are bound and on which the bonding reactions can be detected, and a suction generating absorption region which causes the sample to be tested to flow in a linear manner through the separating membrane.
Test membranes of conventional lateral flow tests are generally described involving a chromatography-like separation. The analyte in the sample bonds specifically to the bonding elements fixed in a membrane which as a rule are present in consecutive or superimposed bands serving as indicator zones. The bonding complex is rendered visible by indicator particles which as a rule are already present in the device in dehydrated form in a conjugate liberation pad. The conjugate liberation pad is typically provided between the application zone and the membrane. The pre-coated colored indicator particles are coated for example with an antibody directed against the analyte to be tested for.
The conventional lateral flow test format corresponds to a so-called “sandwich assay”, in which both the indicator zone as well as the indicator particles are coated with a ligand aimed at the analyte tested for, normally an antibody. In that context the ligand (bonding element) is immobilized on the membrane. The detector reagent, normally an antibody bonded to a colored polystyrene particle or to colloidal metals, is deposited in the conjugate liberation pad in a leachable manner. This bonding complex serves as indicator particle. Once the sample to be tested has been applied it very rapidly wets the conjugate liberation pad, whereby the indicator particles are mobilized. The indicator particles migrate with the liquid front along the porous membrane. An analyte present in the sample becomes bonded by the antibody coupled to the indicator particle. As the sample passes the indicator zone, the analyte/indicator particle complex in the indicator zone is immobilized by reaction of the analyte with the antibody bonded in the indicator zone, resulting in a visible signal.
A further known test format for small analytes comprising but a single antigenic determinant, incapable of simultaneously bonding two antibodies, is the so-called “competition assay”. The detector reagent bonded to the indicator particle is normally a molecule identical to or analogous with the analyte. The indicator particles are deposited in the conjugate liberation pad. The indicator particles migrate with the liquid front along the porous membrane. If the sample contains the analytes, and if the indicator particles (which effectively likewise contain analyte) pass the indicator zone, part of the analyte molecules in the sample bond to part of the indicator particles. The more analyte is present in the sample the more effective will it compete with the bonding of the indicator particle and the weaker will the signal become.
According to the prior art these indicator particles are predominantly composed of colloidal gold or of polystyrene, manufactured and coated according to methods known to the skilled person. In the typical lateral flow test formats the analytes are determined indirectly. In this context a direct determination of an analyte denotes that the analyte is already bonded naturally to the indicator particle (e.g. erythrocyte). In the more common situation of indirect determination of the analytes the sample to be tested as a rule contains a non-cellularly bonded, e.g. plasmatic component as the analyte and, besides the sample to be tested, two reagent components are required, i.e. indicator particles and a bonding element. In the indirect determination the analyte initially bonds to the indicator particle dissolved out of the conjugate liberation pad, before this complex becomes immobilized in the indicator zones with the bonding element by way of a second reaction.
When using conventional lateral flow tests with erythrocytes as indicator particles which have been bonded to the analytes to be determined, for example blood group specific antigens, it is at present usual for antibodies to be provided in the indicator zones against corresponding blood group antigens serving as bonding elements in successive or superimposed bands in but a single flow track such as for example anti-A, anti-B against the Rh blood group system. In this context conventional lateral flow tests suffer from the disadvantage that the erythrocytes bonded to the antibodies form a flow barrier against the analytes still to be tested for, for example further cell associated antigens, in a sample. Due to agglutination or adsorption of cells in a band of bonding elements arranged proximally to the application zone, additional analytes, in particular associated with cells or cell fragments in the sample to be tested, can no longer be separated unimpededly and visibly and can therefore not be tested for unambiguously or completely. For example in a person who is blood group AB Rh D positive this may result in a weakening or elimination of the B and the D bands, which may result in a faulty interpretation of being blood group A Rh negative. For that reason it was hitherto not possible, specifically in blood group serological diagnostics to employ a lateral flow test with more than one indicator zone. In order to determine a plurality of, in particular cellular and plasmatic blood group parameters, it is to date necessary to conduct single parameter tests separately.